Apparatuses, methods, computer programs, and computer program products for interference avoidance

ABSTRACT

A scheduling function node (SF) uses the beams available for each WCD to avoid scheduling a transmission that would imply that interference between WCDs is created. In the simplest form such a scheme could be described as follows: (1) avoid scheduling transmission in directions that coincide between WCDs (here, a direction would typically be represented by both azimuth and elevation angles) and (2) when the available beam directions do not allow interference avoidance, accounting for this fact and exploiting other types of orthogonality in the scheduling of time-frequency resources.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a 35 U.S.C. § 371 National Stage of InternationalPatent Application No. PCT/SE2017/050405, filed Apr. 25, 2017,designating the United States, which is incorporated by reference.

TECHNICAL FIELD

Disclosed are embodiments related to interference avoidance incommunication systems that employ beamforming.

BACKGROUND

1. Beamforming

The next generation mobile wireless communication system, which isreferred to as “5G,” will support a diverse set of use cases and adiverse set of deployment scenarios. 5G will encompass an evolution oftoday's 4G LTE (Long Term Evolution) networks and the addition of a new,globally standardized radio-access technology known as “New Radio” (NR).

The diverse set of deployment scenarios includes deployment at both lowfrequencies (100s of MHz), similar to LTE today, and very highfrequencies (mm waves in the tens of GHz). At high frequencies,propagation characteristics make achieving good coverage challenging.One solution to the coverage issue is to employ beamforming (e.g.,high-gain beamforming) to achieve satisfactory link budget.

Beamforming is an important technology in future radio communicationsystems. It can improve performance both by increasing the receivedsignal strength, thereby improving the coverage, and by reducingunwanted interference, thereby improving the capacity. Beamforming canbe applied both in a transmitter and a receiver.

In a transmitter, beamforming involves configuring the transmitter totransmit the signal in a specific direction (“beam”), or in two or moredirections, and not in other directions. In a receiver, beamforminginvolves configuring the receiver to receive signals from a certaindirection (or a few directions) and not from other directions. Whenbeamforming is applied in both the transmitter and the receiver for agiven communication link, the combination of the beam used by thetransmitter to transmit a signal to the receiver and the beam used bythe receiver to receive the signal is referred to as a beam-pair link(BPL). Generally, the beamforming gains are related to the widths of theused beams: a relatively narrow beam provides more gain than a widerbeam. A BPL can be defined for DL and UL separately or jointly based onreciprocity assumptions.

For a more specific description of beamforming, one typically talksabout beamforming weights rather than beams. On the transmission side,the signal to be transmitted is multiplied with beamforming weights(e.g., complex constants) before being distributed to the individualantenna elements. There are separate beamforming weights for eachantenna element, which allows maximum freedom in shaping thetransmission beam given the fixed antenna array. Correspondingly, on thereceiving side, the received signal from each antenna element ismultiplied separately with the beamforming weights before the signalsare combined. However, in the context of the present text, thedescription is easier to follow if the somewhat simplified notion ofbeams, pointing in certain physical directions, is adopted.

Beamforming is a mature subject today. This section just aims atpresenting the basics. Referring now to FIG. 1, FIG. 1 shows anidealized one-dimensional beamforming case. In case it is assumed that awireless communication device (WCD) (e.g., a user equipment (UE), suchas a smartphone, laptop, tablet, phablet etc.; a machine-typecommunication device, such as a smart appliance, a sensor, etc.; orother device capable of wireless communication) is located far away fromthe antenna array it follows that the difference in travel distance fromthe base station to the WCD, between adjacent antenna elements, is l=kλsin(θ), where kλ is the antenna element separation. Here k is theseparation factor which may be 0.5-0.7 in a typical correlated antennaelement arrangement. This means that if a reference signal s_(i)e^(jωt)transmitted from the i:th antenna element will arrive at the WCD antennaas a weighted sum

$s_{UE} = {{\sum\limits_{i = 0}^{N - 1}{s_{i}h_{i}e^{j\;{\omega{({t - \frac{il}{c}})}}}}} = {{e^{j\;\omega\; t}{\sum\limits_{i = 1}^{N - 1}{s_{i}h_{i}e^{{- j}\frac{{ik}\;{{\lambda\sin}{(\theta)}}}{f_{c}\lambda}}}}} = {e^{j\;\omega\; t}{\sum\limits_{i = 1}^{N - 1}{s_{i}h_{i}{e^{{- j}\frac{{ik}\;{\sin{(\theta)}}}{f_{c}}}.}}}}}}$

Here ω is the angular carrier frequency, h_(i) is the complex channelfrom the i:th antenna element, t is the time, and f_(c) is the carrierfrequency. In the above equation θ and h_(i) are unknown. In case of afeedback solution, the WCD therefore needs to search for all complexchannel coefficients h_(i) and the unknown angle θ. For this reason thestandard defines a codebook of beams in different directions given bysteering vector coefficients like w_(m,i)=e^(−jf(m,i)), where mindicates a directional codebook entry. The WCD then tests each codebookand estimates the channel coefficients. The information rate achievedfor each codebook entry m is computed and the best one defines thedirection and channel coefficients. This is possible since s_(i) isknown. The result is encoded and reported back to the base station. Thisprovides the base station with a best direction (codebook entry) andinformation that allows it to build up a channel matrix H. This matrixrepresents the channel from each of the transmit antenna elements toeach of the receive antenna elements. Typically, each element of H isrepresented by a complex number.

The channel matrix can then be used for beamforming computations, or thedirection represented by the reported codebook entry can be useddirectly. In case of MIMO transmission the MIMO beamforming weightmatrix W needs to be determined so that a best match to the requirementWH=I is achieved where I denotes the identity matrix. In case of anexact match each layer will become independent of other layers. Thisconcept can be applied for single users or multiple users.

When reciprocity is used the channel coefficients can, in principle, bedirectly estimated by the base station from WCD uplink transmission. Socalled sounding reference signals, SRS, are used for this purpose. Theestimated channel is then used to compute the combining weight matrixaccording to some selected principle, and then used for downlinktransmission. This works since the uplink and downlink channels areessentially the same when reciprocity is applicable.

2. 5G 3GPP Reference Signals Supporting Beamforming

Some of the description herein is given in terms of the 3GPP terminologyfor the 4G LTE system, since the standardization of the 5G counterpartsis not yet finalized. The operation of the 5G functionality is expectedto be essentially the same as in the 4G system.

The channel state information reference signals, CSI-RS, which has beenavailable since release 11, are assigned to a specific antenna port.These reference signals may be transmitted to the whole cell or may bebeamformed in a WCD specific manner. In 3GPP from release 13 two classesof CSI-RS reporting mode has been introduced: class A CSI-RS refers tothe use of fixed-beam codebook based beamforming, while a class B CSI-RSprocess may send beamformed CSI-RS in any manner.

A CSI-RS process in a WCD comprises detection of selected CSI-RSsignals, measuring interference and noise on a CSI InterferenceMeasurement (CSI-IM) resource, and reporting of the related CSIinformation, in terms of CQI, RI and PMI. Here CSI denotes channel stateinformation, CQI denotes channel quality indication, RI denotes (channelmatrix) rank indications and PMI denotes pre-coder matrix index, i.e.the selected codebook entry. A WCD may report more than one set of CQI,RI and PMI, i.e. information for more than one codebook entry. Up to 4CSI-RS processes can be set up for each WCD, starting in 3GPP release11.

3. 5G 2D Codebooks and Antenna Port Relations

As stated above the codebook of the 3GPP standard is defined torepresent certain directions. In release 13, directions in both azimuthand elevation is defined, thereby allowing 2D beamforming to be used.These 4G codebooks are specified in detail in 3GPP TR 36.897. A similardefinition, but with finer granularity is expected for the 3GPP 5Gstandard.

In order to illustrate that the codebooks indeed define specificdirections, it can be noted that the formula for the azimuth codebook is

${w_{k} = {{\frac{1}{\sqrt{K}}{\exp( {{- j}\frac{2\pi}{\lambda}( {k - 1} )d_{V}\cos\;\theta_{etilt}} )}\mspace{14mu}{for}\mspace{14mu} k} = 1}},\ldots\mspace{14mu},{K.}$

It has the same structure as discussed above. Similarly, the verticalcodebook in that document is given by

${v_{l,i} = {{\frac{1}{\sqrt{L}}{\exp( {{- j}\frac{2\pi}{\lambda}( {l - 1} )d_{H}\sin\;\vartheta_{i}} )}\mspace{14mu}{for}\mspace{14mu} l} = 1}},\ldots\mspace{14mu},{L.}$

In the two above equations it is only the structure that is needed here,the details of the involved quantities is of less importance and is notreproduced here, see 3GPP TR 36.897 for all details. Finally, it isnoted that a 2D beam is obtained by a multiplication of the two aboveequations.

4. Interference Avoidance with RAIT

Reciprocity-assisted interference aware transmission (RAIT) is atechnique that is applicable primarily for Time Division Duplex (TDD)deployments, where channel reciprocity can be used. Briefly, RAIT offersa unified approach to single point techniques like MU-MIMO andbeamforming, and to multi-point techniques like CoMP and D-MIMO. The keyto achieve this is availability of a high fidelity multi-antenna elementspatial 1D or 2D matrix channel estimate H. Since reciprocity isnormally assumed to hold for RAIT, the channel matrix can be estimatedby application of e.g. sounding reference signals (SRS) in the uplink.The channel matrix is then also valid for downlink transmission. Byformulation of a criterion that embeds the above techniques as specialcases, a combining weight matrix W can then be computed and used tosteer the downlink transmit power in an optimal way. One particularfeature of RAIT is that it is capable to avoid transmission indirections where interference is likely to be created, between users.

SUMMARY

As noted above, in the coming 5G cellular systems, beamforming will be acentral technology. The reason is that spectral resources are runningout at low carrier frequencies which leads to a gradual migration intothe mmw band. There beamforming and a use of massive antenna arrays areneeded to achieve a sufficient coverage. There is available spectrumaround 28 GHz and 39 GHz in the US and other markets, and this spectrumneeds to be exploited to meet the increasing capacity requirements. The5G frequency migration is expected to start at 3.5-5 GHz, and thencontinue to these soon available 28 GHz and 39 GHz bands.

Two main methods are available for wireless beamforming. The firstmethod relies on the downlink and uplink utilizing the same frequencyband. Then channel reciprocity persists and a matrix channel estimatedfor the uplink can be used for optimal beamforming in the downlink,requiring e.g. the beamforming weights forMultiple-Input-Multiple-Output (MIMO) to meet the equation WH=I, where His the channel matrix. The other method relies on reference signalsbeing transmitted from the base station, and by feedback information onsignal quality being sent back from the WCD. In the 4G LTE standard theWCD typically measures the channel response and reports the result backto the base station in terms of CQI, RI and PMI, these quantitiesrepresenting the quality (SNR related), channel rank, and preferredpre-coder, respectively. This is denoted channel state information (CSI)feedback. A similar development, with richer codebooks, is currentlybeing developed for the 5G mmw standards.

One problem that arises with beamforming is interference. For example,it may be the case that the beams of two or more WCDs coincide, in whichcase the WCDs will create interference in case they are scheduledindependently of each other, in the same physical resource blocks but indifferent layers. This disclosure aims to address this problem. Forexample, this disclosure describes, among other things, techniques foravoiding interference in communication systems that use high mmwfrequency bands where digital beamforming algorithms like the RAITalgorithm may not be suitable.

Another problem that may be addressed by some embodiments is associatedwith the estimation of an as good as possible channel model, withoutapplication of reciprocity. Again, this is associated with the UL/DLpower unbalance that increase above 6-10 GHz. Since the codebooks aboverepresent single directions, a single codebook entry is not capable torepresent signal energy from multiple directions, where the angulardifferences between directions are larger than the beam width. Thismeans that useful energy in other directions may not be collected, whichis negative for the possibility to transmit in interference avoidingdirections. Note that such situations are not uncommon e.g. in citiesand indoor environments where a LOS connection may not be available,leaving the communication to rely on multiple reflected paths.

A further problem that may be addressed by some embodiments occurs incase of an established single beam connection between a base station anda WCD. At least when narrow beams are used, the beam and transmissionquality could deteriorate rapidly in case transmission to an interferingWCD in the same direction occurs. The dropped call probability is likelyto increase with the inverse of the beam width, simply the interferingbeam power may become substantial.

Still another problem is associated to the computational complexityassociated with an implementation of RAIT on mmw frequency bands. Theremassive beam forming gains will be needed to achieve a sufficientcoverage. Now, RAIT has a computational complexity that is proportionalto the number of antenna elements of the antenna array, raised to thepower of three. At low band antenna array sizes of 32 to 64 will betypical initially, and then RAIT is on the limit of being implementable.At mmw bands antenna sizes ranging from 128 to at least 512 antennaelements are expected, this being about a factor of 10 higher than atlow bands. The computational complexity at high mmw bands couldtherefore be 10^3=1000 times higher than at low bands, due to this factalone. In addition, the channel decorrelation time in mobility istypically equal to the time it takes for the mobile to travel half awavelength. Therefore, the channel decorrelation times are about tentimes less at high mmw frequencies than at low bands. This means thatRAIT computations will have to be completed 10 times faster than at lowbands in case reciprocity is to be used. This fact may add to thecomputational complexity of RAIT at high bands. To summarize, RAITcomplexity could be more than 1000 times as computationally intense atmmw bands as compared to low bands. This would then make RAIT impossibleto implement at mmw bands, at least in basic form.

In one aspect there is provided a method for interference avoidance. Insome embodiments, the method includes a network node (e.g., a basestation or other network node) obtaining first candidate beaminformation identifying a first set of one or more candidate beams for afirst wireless communication device (WCD) being served by the networknode, the first set of candidate beams for the first WCD comprising afirst candidate beam having a first direction. The method furtherincludes the network node obtaining second candidate beam informationidentifying a second set of one or more candidate beams for a second WCD(390) being served by the network node, the second set of candidatebeams for the second WCD comprising a second candidate beam having asecond direction. The network node uses the first and second candidatebeam information to schedule i) the transmission of first data to thefirst WCD and ii) the transmission of second data to the second WCD. Thescheduling of the transmissions comprises: selecting a transmissionresource for use in transmitting the first data to the first WCD,selecting a transmission resource for use in transmitting the seconddata to the second WCD, and determining whether the first direction isdifferent than the second direction.

In some embodiments, selecting a transmission resource for use intransmitting the first data to the first WCD comprises selecting one ormore of: i) a time slot during which the transmission of the first datato the first WCD will occur and ii) a frequency band in which thetransmission of the first data to the first WCD will occur, andselecting a transmission resource for use in transmitting the seconddata to the second WCD comprises selecting one or more of: i) a timeslot during which the transmission of the second data to the second WCDwill occur and ii) a frequency band in which the transmission of thesecond data to the second WCD will occur. Selecting the transmissionresource for use in transmitting the first data to the first WCD mayfurther comprise selecting a candidate beam from the first set ofcandidate beams for the first WCD; and selecting the transmissionresource for use in transmitting the second data to the second WCD mayfurther comprise selecting a candidate beam from the second set ofcandidate beams for the second WCD.

In some embodiments, scheduling i) the transmission of first data to thefirst WCD and ii) the transmission of second data to the second WCDusing the first and second candidate beam information comprises: usingthe first and second candidate beam information to determine whether itis feasible to select the same time and frequency resources for thetransmission of the first data to the first WCD and the transmission ofthe second data to the second WCD. In some embodiments, the step ofusing the first and second candidate beam information to determinewhether it is feasible to select the same time and frequency resourcescomprises: determining whether there is at least one beam included inthe set of candidate beams for the first WCD that is not included in theset of candidate beams for the second WCD; and determining whether thereis at least one beam included in the set of candidate beams for thesecond WCD that is not included in the set of candidate beams for firstWCD. As a result of determining that it is feasible to select the sametime and frequency resources, the network node may select a time andfrequency resource for the transmission of the first data and select forthe second transmission the same time and frequency resources that areselected for the transmission of the second data.

In some embodiments, selecting a candidate beam from the first set ofcandidate beams for the first WCD comprises: 1) determining a firstsubset of candidate beams for the first WCD, wherein each candidate beamincluded in the first subset of candidate beams is a) included in thefirst set of candidate beams and b) not included in the second set ofcandidate beams; and 2) selecting a candidate beam from the first subsetof candidate beams. In some embodiments, selecting a candidate beam fromthe second set of candidate beams for the second WCD comprises: 1)determining a second subset of candidate beams for the second WCD,wherein each candidate beam included in the second subset of candidatebeams is a) included in the second set of candidate beams and b) notincluded in the first set of candidate beams; and 2) selecting acandidate beam from the second subset of candidate beams.

In some embodiments, the first beam is defined by a codebook entryidentified by a pre-coder matrix index; and the method furthercomprises: a) the network node using the first beam to transmit areference signal and b) the network node receiving from the first WCDfirst channel state information comprising the pre-coder matrix indexand first channel quality information. In some embodiments, the networknode is a base station having more antenna elements than antenna ports,and the method further comprises: a) the network node using a third beamto transmit the reference signal, wherein the third beam is associatedwith the pre-coder matrix index, b) after transmitting the referencesignal using the third beam, the network node receiving from the firstWCD second channel state information comprising the pre-coder matrixindex and second channel quality information, and c) the network nodedetermining whether to add the third beam to the first set of candidatebeams based on the second channel quality information received from thefirst WCD.

In some embodiments, the method also includes: a) the network node usinga fourth beam to transmit the reference signal, wherein the fourth beamis associated with the pre-coder matrix index, b) after transmitting thereference signal using the fourth beam, the network node receiving fromthe first WCD third channel state information comprising the pre-codermatrix index and third channel quality information, and c) the networknode determining whether to add the fourth beam to the first set ofcandidate beams based on the third channel quality information receivedfrom the first WCD. The third beam is angularly shifted with respect tothe first beam in a first direction, and the fourth beam is angularlyshifted with respect to the first beam in a second direction.

In some embodiments, the method also includes the network node obtainingthe first data for transmission to the first WCD; and the network nodeobtaining the second data for transmission to the second WCD.

Advantages

A principle advantage of embodiments described herein includes improvedcapacity and reduced interference. Other advantages include: 1) backwardcompatible solution, including LTE releases from release 11; 2) optimaluse of more spatial dimensions, when feedback type beamforming isapplied; 3) resource efficient background beam scan, by the use of cellspecific CSI-RS for the scan, allowing all WCDs to share the scanresource; 4) a much smaller computational complexity than RAIT at highmmw bands. Also, embodiments can be used in situations without channelreciprocity assistance, thereby complementing RAIT.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments.

FIG. 1 shows an idealized one-dimensional beamforming case.

FIG. 2 depicts an ongoing communication process between a base stationand a WCD.

FIG. 3 illustrates a reflected path to a WCD.

FIG. 4 illustrates a case when the scheduler detects that directions arenot available for interference avoidance between WCDs

FIG. 5 illustrates oversampling.

FIG. 6 is a flow chart illustrating a process according to someembodiments.

FIG. 7 is a block diagram of a computer apparatus according to someembodiments.

FIG. 8 is a diagram showing functional modules of a network nodeaccording to some embodiments.

DETAILED DESCRIPTION

FIG. 2 depicts a communication process between a base station 102 and aWCD 104. In this illustration, one beam (i.e., beam 202) is used thatutilizes a line-of-sight (LOS) propagation path. A WCD-specific CSI/RSprocess is used to support the transmission. The exact beam formerapplied may be based on the exact codebook directions fed back when thebeam was first searched for. Note that in case a wider beam was used forthis search, the feedback would have provided a more precise beamdirection, via PMI feedback.

FIG. 3 shows an example in which WCD 104 can also be reached with areflected beam 302. That direction has not yet been detected in the WCD.However, the proposed beam scan function is operating in the backgroundby a second cell specific CSI-RS process common for all WCDs in thecell. WCD 104 measures the signal on the cell-specific CSI-RS processand reports back CQI, while the base station transmits the CSI-RS signalat the same configured occasions. In this way the WCD 104 can finallydetect signal energy in the new direction, and a secondary beam may beadded, by assigning another WCD specific CSI-RS process.

A scheduling function node (SF) 306 uses the multiple beam directionsavailable for each WCD to avoid a scheduling decision that would implythat interference between WCDs is created. In the simplest form such ascheme could be described as follows: (1) avoid scheduling transmissionin directions that coincide between WCDs (here, a direction wouldtypically be represented by both azimuth and elevation angles) and (2)when the available beam directions do not allow interference avoidance,accounting for this fact and exploiting other types of orthogonality inthe scheduling of time-frequency resources. More advanced schemes, thatweigh the estimated amount of created interference against the gainassociated with using transmit directions with a high channel gain canof course also be used. While SF 306 is shown in FIG. 3 as beingseparate and apart from base station 102, this is not a requirement asSF 306 may be a component of base station 102.

FIG. 3 illustrates a case were beamformed directions are available thatallows interference avoiding downlink transmission to take place. Morespecifically, FIG. 3 shows that beam 302 can be used by base station 102to transmit data to WCD 104 and further shows that a different beam(beam 303) can be used by base station 102 to simultaneously transmitdata to WCD 390 (the transmission to WCD 390 may also use the samefrequency resources as the simultaneous transmission to WCD 104 becausethe beam 303 used for transmitting the data to WCD 390 has a lowlikelihood of interfering with the beam 302 used to transmit the data toWCD 104 because the two beams follow different paths). FIG. 4illustrates a case when the scheduler detects that different beams arenot available for interference avoidance between WCDs 104 and 390, andwhere the scheduler schedules WCDs 104 and 390 to disjoint parts of thetime-frequency resource grid. In other words, because the only beamavailable for WCD 104 (i.e., beam 402) is a beam that would also bereceived by WCD 390, the scheduler may determine that the best way toavoid interference is to schedule WCD 104 and WCD 390 such that thescheduled transmissions are not performed at the same time and/or arenot performed using the same frequency resources.

As illustrated above, by making use of information that identifies thebeams that are available for each WCD, the SF 306 is able to scheduletransmissions to two more WCDs such that the transmissions occur usingthe same time and frequency resources, but using different beams,thereby reducing the likelihood of interference yet also increasingsystem capacity. The following describes one way in which base station102 can determine available beams for each WCD that is being served bythe base station 102.

Beam Search

Base station 102 selects a set of cell specific CSI-RS processes andperforms setup of a beam scan pattern, on the time-resource grid used in5G. The beam scan pattern may be selected to be a sequence of beamsselected from the code book of the standard. The WCDs that are subjectto beam scan are selected, according to selected priorities, theservice, or another criterion. Note that all WCDs may not be subject tobeam scan. The selected WCDs are configured with at least a subset ofthe cell specific set of CSI-RS processes. The selected reportingoptions are also configured. This may comprise a reporting of more thanone beam direction per reporting instance. The following steps are thenrepeated: 1) the base station transmit the cell specific CSI-RSsaccording to the selected scan pattern, 2) the WCDs configured with theappropriate cell specific CSI-processes, perform CSI-RS detection,reporting CSI information in line with the 3GPP 5G standard, 3) the CSIfeedback information is received in the base station, for each WCDconfigured with the cell-specific CSI-RS processes in question, 4) Thebase station uses the received feedback information to update thechannel matrix for each WCD configured with the cell-specific CSI-RSprocesses, 5) the base station may determine to add beam directions withsufficiently high energy to ongoing beamformed transmissions, 6) thebase station computes new beam forming/transmission weights for allWCDs, and continues transmission according to the weights, 7) the basestation may configure beam scan for additional WCDs, and/or removeexisting configurations of beam scan, from WCDs currently being subjectto a beam scan.

Refined Beam Search

In case the number of antenna elements is larger than the number ofantenna ports, the beamwidth and antenna gain offered by the codebookcan be reduced and increased, respectively. This requires using theavailable antenna elements to do beamforming in a more advantageousdirection than offered by the selected codebook entry.

In order to find such a direction a spatial oversampling procedure issuggested here. The oversampling is illustrated by FIG. 5. In FIG. 5 itis assumed that there are more antenna elements than antenna ports.Spatial oversampling then allows beams to be formed with directions oneach side of a beam 502 defined by a codebook entry. The base station102 then schedules subsequent beamformed transmissions in theseoversampled directions (e.g., beams 504, 505, 506, and 507), andcollects CSI-information from WCD 104. This search uses each of the WCDspecific CSI-RS processes that have been obtained from the beam searchabove. The best CQI is used as an indication of a best oversampleddirection. This direction is selected for beamforming ahead in time. Forexample, the base station 102 may transmit the CSI-RS using beam 504 andthen wait to receive a CSI report from the WCD. Base station 102 canrepeat this step for each of beams 505-507 and then select one of thebeams 504-507 or beam 502 depending on the CSI information received andadd the selected beam to a set of candidate beams for WCD 104. The basestation can then use the set of candidate beams for WCD 104 to make ascheduling decision as described below.

For example, in an embodiment the network node uses beam 502 (i.e., a“first” beam) to transmit a reference signal, wherein beam 502 isdefined by a codebook entry identified by a pre-coder matrix index; andthe network node receives from WCD 104 first channel state informationcomprising the pre-coder matrix index and first channel qualityinformation. The network node then uses beam 504 to transmit thereference signal, wherein beam 504 is associated with the pre-codermatrix index. After transmitting the reference signal using beam 504,the network node receives from WCD 104 second channel state informationcomprising the pre-coder matrix index and second channel qualityinformation. The network node then uses beam 505 to transmit thereference signal, wherein beam 505 is associated with the pre-codermatrix index. After transmitting the reference signal using beam 505,the network node receives from WCD 104 third channel state informationcomprising the pre-coder matrix index and third channel qualityinformation. The network node determines whether to add one of beams502, 504 and 505 to the first set of candidate beams based on thechannel quality information received from WCD 104. Preferably, beam 504is angularly shifted with respect to beam 502 in a first direction, andbeam 505 is angularly shifted with respect to beam 502 in a seconddirection.

Scheduling DL Transmissions to Minimize Interference

For each WCD that is subject to joint directional interference awarescheduling, the PMIs and CQIs for each detected beam direction for theWCD is tracked. The PMIs define the directions to each WCD, while theCQIs define the corresponding channel quality, typically in terms of SNRor power. Using this information, the base station 102 can define forthe each of the WCDs a set of one or more candidate beams for use intransmitting DL data to the WCD.

At each scheduling opportunity, the SF 306 selects transmissionresources (e.g., beams, time slots, and frequencies) for each WCD, bymeans of an algorithm sensitive to the above PMI and CQI quantities, sothat each WCD is scheduled to avoid interfering other users, when thisis advantageous according to the scheduling algorithm, and possibly anunderpinning criterion. The basic principles are depicted in FIG. 3 andFIG. 4, as described above. Many scheduling algorithms are possible.Traditional sequential ad hoc algorithms can, for example, be re-used,starting with a subset of WCDs at a time and testing all alternativebeams for the subset, while using previous functionality fortime-frequency scheduling. Alternatively, new joint criteria could bedefined, followed by a solution to obtain optimal scheduling decisions.Also, the scheduling algorithms may be extended to cover clusters ofcells, as in Ericsson's eRAN solution

FIG. 6 is a flow chart illustrating a process 600 according to someembodiments. Process 600 may begin with step 602, in which a networknode (i.e., base station 102 or another node that implements SF 306)obtains first candidate beam information identifying a first set of oneor more candidate beams for WCD 104 (i.e., a “first” WCD that is beingserved by the network node 102,306). The first set of candidate beamsfor WCD 104 comprising a first candidate beam having a first direction.

In step 604, the network node obtains second candidate beam informationidentifying a second set of one or more candidate beams for WCD 390(i.e., a “second” WCD that is being served by the network node). Thesecond set of candidate beams for WCD 390 comprises a second candidatebeam having a second direction.

In step 606, the network node obtains first data for transmission to WCD104. In step 608, the network node obtains second data for transmissionto WCD 390. Steps 606 and 608 are optional in scenarios in which SF 306is not a component of base station 102. That is, in some embodiments, SF306 performs all of the steps of FIG. 6 except steps 606 and 608, whichare performed by base station 102.

In step 610, the network node, using the first and second candidate beaminformation, schedules i) the transmission of the first data to WCD 104and ii) the transmission of the second data to WCD 390. The schedulingof the transmissions comprises: selecting a transmission resource foruse in transmitting the first data to WCD 104, selecting a transmissionresource for use in transmitting the second data to WCD 390, anddetermining whether the first direction is different than the seconddirection.

For example, if it is determined that: i) the candidate beams for theWCD 104 includes only a first beam having a first direction (e.g., beam302), ii) the candidate beams for the WCD 390 includes only a secondbeam having a second direction (e.g., beam 303), and iii) the firstdirection is different than the second direction, then it may befeasible for the network node to select the same time and frequencyresources for the respective transmissions to WCD 104 and WCD 390because the first beam can be used to transmit the data to WCD 104, thesecond beam can be used to transmit the data to WCD 390, and the twobeams will not interfere with each other.

As another example, if it is determined that: i) the candidate beams forthe WCD 104 includes only a first beam having a first direction (e.g.,beam 402 a), ii) the candidate beams for the WCD 104 includes a secondbeam having a second direction (e.g. beam 403) and a third beam having athird direction (e.g., beam 402 b) that is the same as the firstdirection (i.e., the direction of the first beam 402 a is the same asthe direction of the third beam 402 b), then it would not be advisablefor the network node to select the same time and frequency resources forthe respective transmissions to WCD 104 and WCD 390 because the onlybeam that is available for the transmission to WCD 104 is beam 402 a,which beam would also be received by WCD 390, thereby potentiallycausing interference. This example is illustrated in FIG. 4.

More generally, if: a) there is at least one beam included in thecandidate beams for WCD 104 that is not included in the candidate beamsfor WCD 390 and b) there is at least one beam included in the candidatebeams for WCD 390 that is not included in the candidate beams for WCD104, then it may be feasible for the network node to select the sametime and frequency resources for the respective transmissions to WCD 104and WCD 390. This example is illustrated in FIG. 3, which shows that theset of candidate beam for WCD 104 includes beams 302 and 304 a and theset of candidate beam for WCD 390 includes beams 303 and 304 b. That is,as shown in FIG. 3, there is at least one beam included in the candidatebeams for WCD 104 that is not included in the candidate beams for WCD390 (i.e., beam 302) and there is at least one beam included in thecandidate beams for WCD 390 that is not included in the candidate beamsfor WCD 104 (i.e. beam 303).

Accordingly, step 610 may include using the first and second candidatebeam information to determine whether it is feasible to select the sametime and frequency resources for the transmission of the first data toWCD 104 and the transmission of the second data to WCD 390. And thisstep of using the first and second candidate beam information todetermine whether it is feasible to select the same time and frequencyresources may include: determining whether there is at least one beamincluded in the set of candidate beams for WCD 104 that is not includedin the set of candidate beams for WCD 390; and determining whether thereis at least one beam included in the set of candidate beams for WCD 390that is not included in the set of candidate beams for WCD 104. In someembodiments, as a result of determining that it is feasible to selectthe same time and frequency resources, the network node selects a timeand frequency resource for the transmission of the first data andselects for the second transmission the same time and frequencyresources that are selected for the transmission of the second data.

In some embodiments, selecting a transmission resource for use intransmitting the first data to WCD 104 comprises selecting one or moreof: i) a time slot during which the transmission of the first data toWCD 104 will occur and ii) a frequency band in which the transmission ofthe first data to WCD 104 will occur, and selecting a transmissionresource for use in transmitting the second data to WCD 390 comprisesselecting one or more of: i) a time slot during which the transmissionof the second data to WCD 390 will occur and ii) a frequency band inwhich the transmission of the second data to WCD 390 will occur.Selecting the transmission resource for use in transmitting the firstdata to WCD 104 may further comprise selecting a candidate beam from thefirst set of candidate beams for WCD 104, and selecting the transmissionresource for use in transmitting the second data to WCD 390 may furthercomprise selecting a candidate beam from the second set of candidatebeams for WCD 390. In some embodiments, selecting a candidate beam fromthe first set of candidate beams for WCD 104 comprises: 1) determining afirst subset of candidate beams for WCD 104, wherein each candidate beamincluded in the first subset of candidate beams is a) included in thefirst set of candidate beams and b) not included in the second set ofcandidate beams; and 2) selecting a candidate beam from the first subsetof candidate beams; and selecting a candidate beam from the second setof candidate beams for WCD 390 comprises: 1) determining a second subsetof candidate beams for WCD 390, wherein each candidate beam included inthe second subset of candidate beams is a) included in the second set ofcandidate beams and b) not included in the first set of candidate beams;and 2) selecting a candidate beam from the second subset of candidatebeams.

FIG. 7 is a block diagram of a computer apparatus 700 according to someembodiments for implementing the above described network node 102,306.As shown in FIG. 7, the computer apparatus may comprise: a dataprocessing apparatus (DPA) 702, which may include one or more processors(P) 755 (e.g., a general purpose microprocessor and/or one or more otherprocessors, such as an application specific integrated circuit (ASIC),field-programmable gate arrays (FPGAs), and the like); a networkinterface 748 comprising a transmitter (Tx) 745 and a receiver (Rx) 747for enabling computer apparatus to transmit data to and receive datafrom other nodes connected to a network 110 (e.g., an Internet Protocol(IP) network) to which network interface 748 is connected; and localstorage unit (a.k.a., “data storage system”) 708, which may include oneor more non-volatile storage devices and/or one or more volatile storagedevices (e.g., random access memory (RAM)). In embodiments wherecomputer apparatus includes a general purpose microprocessor, a computerprogram product (CPP) 741 may be provided. CPP 741 includes a computerreadable medium (CRM) 742 storing a computer program (CP) 743 comprisingcomputer readable instructions (CRI) 744. CRM 742 may be anon-transitory computer readable medium, such as, but not limited, tomagnetic media (e.g., a hard disk), optical media, memory devices (e.g.,random access memory), and the like. In some embodiments, the CRI 744 ofcomputer program 743 is configured such that when executed by dataprocessing apparatus 702, the CRI causes computer apparatus to performsteps described herein (e.g., steps described herein with reference tothe flow charts and/or message flow diagrams). In other embodiments,computer apparatus may be configured to perform steps described hereinwithout the need for code. That is, for example, data processingapparatus 702 may consist merely of one or more ASICs. Hence, thefeatures of the embodiments described herein may be implemented inhardware and/or software.

FIG. 8 is a diagram showing functional modules of network node 102, 306according to some embodiments. As shown in FIG. 8, the network nodeincludes an obtaining module 802 and a scheduling module 804. Theobtaining module 802 is configured to: i) obtain first candidate beaminformation identifying a first set of one or more candidate beams forWCD 104 that is being served by the network node, the first set ofcandidate beams for the first WCD comprising a first candidate beamhaving a first direction and 2) obtain second candidate beam informationidentifying a second set of one or more candidate beams for WCD 390 thatis being served by the network node, the second set of candidate beamsfor the second WCD comprising a second candidate beam having a seconddirection. The scheduling module 804 is configured to schedule i) thetransmission of first data to the first WCD and ii) the transmission ofsecond data to the second WCD, wherein the scheduling module isconfigured to perform the scheduling of the transmissions using thefirst and second candidate beam information, and the scheduling of thetransmissions comprises: selecting a transmission resource for use intransmitting the first data to the first WCD, selecting a transmissionresource for use in transmitting the second data to the second WCD, anddetermining whether the first direction is different than the seconddirection.

While various embodiments of the present disclosure are described herein(including the appendices), it should be understood that they have beenpresented by way of example only, and not limitation. Thus, the breadthand scope of the present disclosure should not be limited by any of theabove-described exemplary embodiments. Moreover, any combination of theabove-described elements in all possible variations thereof isencompassed by the disclosure unless otherwise indicated herein orotherwise clearly contradicted by context.

Additionally, while the processes described above and illustrated in thedrawings are shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

The invention claimed is:
 1. A method for interference avoidance,comprising: a network node obtaining first candidate beam informationidentifying a first set of one or more candidate beams for a firstwireless communication device, WCD, being served by the network node,the first set of candidate beams for the first WCD comprising a firstcandidate beam having a first direction; the network node obtainingsecond candidate beam information identifying a second set of one ormore candidate beams for a second WCD being served by the network node,the second set of candidate beams for the second WCD comprising a secondcandidate beam having a second direction; and the network node, usingthe first and second candidate beam information, scheduling i) thetransmission of first data to the first WCD and the transmission ofsecond data to the second WCD, wherein the scheduling of thetransmissions comprises: selecting a transmission resource for use intransmitting the first data to the first WCD, selecting a transmissionresource for use in transmitting the second data to the second WCD,selecting the transmission resource for use in transmitting the firstdata to the first WCD further comprises selecting a candidate beam fromthe first set of candidate beams for the first WCD, and selecting thetransmission resource for use in transmitting the second data to thesecond WCD further comprises selecting a candidate beam from the secondset of candidate beams for the second WCD, selecting a candidate beamfrom the first set of candidate beams for the first WCD comprisesselecting a candidate beam from a first subset of candidate beams,wherein each candidate beam included in the first subset of candidatebeams is a) included in the first set of candidate beams and b) notincluded in the second set of candidate beams, and selecting a candidatebeam from the second set of candidate beams for the second WCD comprisesselecting a candidate beam from a second subset of candidate beams,wherein each candidate beam included in the second subset of candidatebeams is a) included in the second set of candidate beams and b) notincluded in the first set of candidate beams.
 2. The method of claim 1,wherein selecting the transmission resource for use in transmitting thefirst data to the first WCD comprises selecting one or more of: i) atime slot during which the transmission of the first data to the firstWCD will occur and ii) a frequency band in which the transmission of thefirst data to the first WCD will occur, and selecting the transmissionresource for use in transmitting the second data to the second WCDcomprises selecting one or more of: i) a time slot during which thetransmission of the second data to the second WCD will occur and ii) afrequency band in which the transmission of the second data to thesecond WCD will occur.
 3. The method of claim 1, wherein, scheduling i)the transmission of first data to the first WCD and ii) the transmissionof second data to the second WCD using the first and second candidatebeam information comprises: using the first and second candidate beaminformation to determine whether it is feasible to select the same timeand frequency resources for the transmission of the first data to thefirst WCD and the transmission of the second data to the second WCD. 4.The method of claim 3, wherein the step of using the first and secondcandidate beam information to determine whether it is feasible to selectthe same time and frequency resources comprises: determining whetherthere is at least one beam included in the set of candidate beams forthe first WCD that is not included in the set of candidate beams for thesecond WCD; and determining whether there is at least one beam includedin the set of candidate beams for the second WCD that is not included inthe set of candidate beams for first WCD.
 5. The method of claim 4,wherein, as a result of determining that it is feasible to select thesame time and frequency resources, the network node selects a time andfrequency resource for the transmission of the first data and selectsfor the second transmission the same time and frequency resources thatare selected for the transmission of the second data.
 6. The method ofclaim 1, wherein the first beam is defined by a codebook entryidentified by a pre-coder matrix index; and the method furthercomprises: the network node using the first beam to transmit a referencesignal; and the network node receiving from the first WCD first channelstate information comprising the pre-coder matrix index and firstchannel quality information.
 7. The method of claim 6, wherein thenetwork node is a base station having more antenna elements than antennaports, and the method further comprises: the network node using a thirdbeam to transmit the reference signal, wherein the third beam isassociated with the pre-coder matrix index, after transmitting thereference signal using the third beam, the network node receiving fromthe first WCD second channel state information comprising the pre-codermatrix index and second channel quality information, and the networknode determining whether to add the third beam to the first set ofcandidate beams based on the second channel quality information receivedfrom the first WCD.
 8. The method of claim 7, wherein the method furthercomprises: the network node using a fourth beam to transmit thereference signal, wherein the fourth beam is associated with thepre-coder matrix index, after transmitting the reference signal usingthe fourth beam, the network node receiving from the first WCD thirdchannel state information comprising the pre-coder matrix index andthird channel quality information, and the network node determiningwhether to add the fourth beam to the first set of candidate beams basedon the third channel quality information received from the first WCD. 9.The method of claim 8, wherein the third beam is angularly shifted withrespect to the first beam, and the fourth beam is angularly shifted withrespect to the first beam.
 10. The method of claim 1, furthercomprising: the network node obtaining the first data for transmissionto the first WCD; and the network node obtaining the second data fortransmission to the second WCD.
 11. The method of claim 1, wherein thenetwork node is a base station comprising a scheduling function node,SF.
 12. The method of claim 1, wherein the network node comprises ascheduling function node, SF, and the network node is not a basestation.
 13. A network node for interference avoidance, the network nodecomprising: a computer readable medium; and a data processing apparatus,comprising one or more processors, coupled to the computer readablemedium, wherein the data processing apparatus is configured to: obtainfirst candidate beam information identifying a first set of one or morecandidate beams for a first wireless communication device, WCD, beingserved by the network node, the first set of candidate beams for thefirst WCD comprising a first candidate beam having a first direction;obtain second candidate beam information identifying a second set of oneor more candidate beams for a second WCD being served by the networknode, the second set of candidate beams for the second WCD comprising asecond candidate beam having a second direction; and schedule i) thetransmission of first data to the first WCD and ii) the transmission ofsecond data to the second WCD, wherein the data processing system isconfigured to perform the scheduling of the transmissions using thefirst and second candidate beam information, the scheduling of thetransmissions comprises: selecting a transmission resource for use intransmitting the first data to the first WCD, selecting a transmissionresource for use in transmitting the second data to the second WCD, anddetermining whether the first direction is different than the seconddirection, selecting the transmission resource for use in transmittingthe first data to the first WCD further comprises selecting a candidatebeam from the first set of candidate beams for the first WCD selectingthe transmission resource for use in transmitting the second data to thesecond WCD further comprises selecting a candidate beam from the secondset of candidate beams for the second WCD, the network node isconfigured to select a candidate beam from the first set of candidatebeams for the first WCD by: 1) determining a first subset of candidatebeams for the first WCD, wherein each candidate beam included in thefirst subset of candidate beams is a) included in the first set ofcandidate beams and b) not included in the second set of candidatebeams; and 2) selecting a candidate beam from the first subset ofcandidate beams, and the network node is configured to select acandidate beam from the second set of candidate beams for the second WCDby: 1) determining a second subset of candidate beams for the secondWCD, wherein each candidate beam included in the second subset ofcandidate beams is a) included in the second set of candidate beams andb) not included in the first set of candidate beams; and 2) selecting acandidate beam from the second subset of candidate beams.
 14. Thenetwork node of claim 13, wherein, scheduling i) the transmission offirst data to the first WCD and ii) the transmission of second data tothe second WCD using the first and second candidate beam informationcomprises: using the first and second candidate beam information todetermine whether it is feasible to select the same time and frequencyresources for the transmission of the first data to the first WCD andthe transmission of the second data to the second WCD.
 15. The networknode of claim 14, wherein the network node is configured to use thefirst and second candidate beam information to determine whether it isfeasible to select the same time and frequency resources by performing aprocess comprising: determining whether there is at least one beamincluded in the set of candidate beams for the first WCD that is notincluded in the set of candidate beams for the second WCD; anddetermining whether there is at least one beam included in the set ofcandidate beams for the second WCD that is not included in the set ofcandidate beams for first WCD.
 16. The network node of claim 15,wherein, the network node is configured such that, as a result ofdetermining that it is feasible to select the same time and frequencyresources, the network node selects a time and frequency resource forthe transmission of the first data and selects for the secondtransmission the same time and frequency resources that are selected forthe transmission of the second data.
 17. The network node of claim 13,wherein the first beam is defined by a codebook entry identified by apre-coder matrix index; and the network node is further configured to:use the first beam to transmit a reference signal; and receive from thefirst WCD first channel state information comprising the pre-codermatrix index and first channel quality information.
 18. The network nodeof claim 17, wherein the network node is a base station having moreantenna elements than antenna ports, and the network node is furtherconfigured to: use a third beam to transmit the reference signal,wherein the third beam is associated with the pre-coder matrix index,after transmitting the reference signal using the third beam, receivefrom the first WCD second channel state information comprising thepre-coder matrix index and second channel quality information, anddetermine whether to add the third beam to the first set of candidatebeams based on the second channel quality information received from thefirst WCD.
 19. The network node of claim 18, wherein the network node isfurther configured to: use a fourth beam to transmit the referencesignal, wherein the fourth beam is associated with the pre-coder matrixindex, after transmitting the reference signal using the fourth beam,receive from the first WCD third channel state information comprisingthe pre-coder matrix index and third channel quality information, anddetermine whether to add the fourth beam to the first set of candidatebeams based on the third channel quality information received from thefirst WCD, the third beam is angularly shifted with respect to the firstbeam, and the fourth beam is angularly shifted with respect to the firstbeam.
 20. A computer program product comprising a non-transitorycomputer readable medium storing a computer program comprisinginstructions which when executed by a data processing apparatus causesthe data processing apparatus to perform the method of claim 1.